1. Field of the Invention
The present invention relates to a mold-forming component and an associated mold-retaining component which permit mass production of wax patterns used in the lost wax process (cire perdue), such as for manufacture of detailed metal jewelry, and to methods of using such components.
2. Prior Art
The lost wax process can be used to form a metal master model from an original hand-carved wax model. Conventionally, the metal master model is placed in a metal frame which is open at the top and bottom. Soft and pliable rubber material is packed around the master model. Such material then is compressed between hot platens to vulcanize the rubber material and form a more rigid but still resilient rubber block with the master model buried in the block.
The rubber block is removed from the frame and is cut from its circumference inward to the master model until the block can be separated into complemental mold halves. When the master model is removed, the mold halves can be placed back together such that there is a central mold cavity of a shape identical to the shape of the master model.
A sprue extends from the central mold cavity to the exterior of the composite mold. Usually the sprue is formed during the vulcanization process by a stem or "sprue former" which extends outward from the master model to the metal frame.
The resulting resilient reusable mold is used for mass production of wax patterns. More specifically, the mold halves are held together while melted wax is injected through the sprue into the central mold cavity. When the wax has hardened, the mold halves are separated and the wax pattern can be removed. Each wax pattern can be used in the manufacture of the desired metal jewelry item by the lost wax casting process.
The wax patterns must reproduce even the finely detailed features and filigrees of the master model which can include undercuts and small projections of complicated shapes. Hot wax flows more easily into the central cavity of the resilient rubber mold than cooler wax, but hot wax also speeds deterioration of the mold. High-pressure melted wax also will fill the mold cavity more reliably than wax injected at a lower pressure, but high-pressure wax can deform the mold or form undesirable parting lines. The wax casting temperature and pressure must be adjusted depending on the detail of the item to be produced and whatever is considered to be an acceptable proportion of rejects.